1. Field of the Invention
The present invention pertains to apparatus for maintaining the temperature of a liquid. Specifically, the present invention pertains to apparatus for cooling a liquid and/or retarding an increase in liquid temperature, due to external influences. More specifically, the present invention pertains to apparatus suitable for cooling and retarding increases in temperature of water contained in a bait container or vessel.
2. Description of the Prior Art
Both commercial fisherman and those who fish for sport generally prefer live bait, e.g. shrimp, minnows, etc. The live bait is usually placed in a water filled vessel of some type, the water being at a temperature approximating the temperature of the water from which the bait is removed. Many boats are provided with such a vessel, sometimes referred to as a "bait well". Others simply place the live bait in a bucket or some other type of vessel.
Shrimp, minnows and other live bait can only survive with a sufficient oxygen supply and in a habitat of certain temperature ranges. As water temperature increases, the water holds less oxygen. In warm water, the metabolism of cold blooded animals, such as shrimp and fish, tends to speed up, increasing oxygen consumption and toxic waste production. It is therefore necessary, to keep the water cool, preferably around 70.degree. F. in the summer. At this temperature, bait will not only use less oxygen, but the water will more easily absorb oxygen when aerated. If live shrimp are caught or purchased from water at a temperature greater than 70.degree. F., the water in which they are kept should be cooled to as near 70.degree. F. as possible. However, the shrimp should be gradually acclimated to this temperature in the bait container. Shrimp can tolerate a change of 5.degree. F. per half hour. However, a change more abrupt than this will shock the shrimp.
Many fishermen begin fishing early in the morning, the coolest part of the day. However, as the day progresses, the bait well or other vessel containing the bait is subjected to increasing temperatures and in many cases direct exposure to the sun. As this occurs, the temperature of the water in which the bait is contained increases, sometimes by as much as 10.degree. F. to 20.degree. F. Due to the increased metabolism of the bait, increased oxygen consumption and toxic waste production, the bait may die in just two hours. It is common knowledge that dead bait is not as attractive to fish as live bait.
Large commercial fishing vessels may be provided with bait wells which are refrigerated. Such refrigeration systems require a source of power and are relatively expensive, particularly for the small commercial fisherman or the pleasure fisherman. In the past, the most convenient way for the small commercial fisherman or pleasure fisherman to cool the water in which the bait is placed has been to add ice thereto. However, ice melts rapidly and must be continuously replenished. Furthermore, unless the ice is made from a composition of water similar to the water in which the bait is held, the ice water may alter the salinity or other composition of the water in which the bait is held. Although salinity is not as critical as temperature, changes in water composition also contribute to death of the bait. More satisfactory solutions for keeping bait alive over a longer period of time are needed.